Since about the 1950s the majority of the agricultural equipment changed from solid bearings to ball and roller bearings because of the obvious advantages of the construction. Spherical bearings, which are self-aligning, have found many applications in part due to their ability to withstand high radial loads. Ordinarily, spherical bearings do not encounter substantial thrust loads which are axial to this shaft.
One problem which exists in the agricultural machinery industry is that of bearing contamination in many applications. Many pillow blocks and bearing holders are exposed to foliage, dirt, mud, stones, and various other types of debris. These conditions cause foreign materials to enter the bearing when the seal fails. The lubrication of the bearing is then contaminated which causes the bearing to fail due to blockage and improper lubrication.
Since the key to bearing protection is to keep contamination out of the internal moving parts, manufacturers have constantly been developing new and more effective seals. However, many seals are not designed to withstand heavy side pressure of vines and mud and will quickly fail in such applications. Sophisticated bearing seals have been designed in which a triple lip seal is employed. The seal is stationary in relation to the shaft in such seals. Dirt tends to eat the rubber seals out when pushed into the seal at high pressure. Although triple lip seals such as Fafiner brand seals increase the life of a bearing they are expensive and still do not effectively protect the bearing from thrust loads.
Bearing flings have been used to keep dirt from the bearing. Bearing flings are pressed fit onto an extended race bearing. Flings are not able to withstand appreciable side thrust since they are merely intended to throw dirt outwardly away from the seals.
Nilos brand rings are bearing seals which are clamped to a bearing housing such that the Nilos ring does not move. The manufacturer states that Nilos rings cannot be used on bearings which make self-aligning movements such as spherical bearings. Sealing is obtained by the sealing edge rotating under slight pressure against either the inner or outer bearing ring. This results in a shallow groove worn into the hardened bearing ring to produce a miniature labyrinth. Nilos rings require housings for attachment.